Electronic circuits may be damaged by electrostatic discharges occurring at their electrical connection terminals. Such electrostatic discharges may in particular occur when the electronic circuit is handled by an operator or by a handling robot, in particular when fabricating this circuit. It is known to place a device for protecting the circuit against electrostatic discharges at at least some of the terminals of the circuit, so as to prevent the damage caused to the circuit by electrostatic discharges occurring at these terminals.
A protective device known to a person skilled in the art comprises two diodes connected in parallel to one terminal of an electronic circuit, and respectively connecting this terminal to two rails, each one connected to a respective terminal of a DC power source supplying this circuit. One of the diodes has its anode connected to the terminal of the circuit, and its cathode connected to the one of the two rails which has the highest electrical potential, hereinafter the first rail. The other diode has its cathode connected to the terminal of the circuit and its anode connected to the one of the two rails which has the lowest electrical potential, hereinafter the second rail. A voltage-limiting device, called a “clamp” in the jargon of a person skilled in the art, is also connected between the first and second rails. The voltage-limiting device is designed so as to become an electrical conductor with a low ohmic resistance when the electrical voltage between the first rail and the second rail is greater than the voltage of the power source, or is negative.
Thus, electric charges of an electrostatic discharge occurring on said terminal of the circuit are removed by the first rail to the DC power source, when the discharge is positive, and by the second rail when the discharge is negative. The electronic circuit is thus preserved. The two diodes and the two rails must have a high ability to conduct electric currents, so that large numbers of electrical charges can be removed quickly and without excessive heating.
Such a protective device further comprises an external connection terminal electrically linked to the terminal of the electronic circuit. The external connection terminal comprises a conducting region which is large enough to allow electrical connections to be made between this connection terminal and electrical devices external to the electronic circuit. These connections are, for example, made by metal wires soldered to the external connection terminal.
Both diodes of such a protective device made on a substrate of an integrated electronic circuit are placed at the side of the external connection terminal, to which they are electrically connected. Overall, the protective device consequently occupies a region of the substrate which is at least equal to the combination of the region of substrate occupied by the connection terminal itself and the region of the substrate occupied by the two diodes.
The result of this is that such a device for protecting against electrostatic discharges occupies a relatively large area of the substrate. In general, an integrated electronic circuit comprises several terminals, each one having to be protected against electrostatic discharges, so that all the protective devices of the electronic circuit require a particularly large area of the substrate. Correlatively, an electronic circuit protected in this way against electrostatic discharges therefore has a high cost.